Method of lubricating transport systems or parts thereof, and also the use of a lubrication arrangement for carrying out the method, and an associated transport system with corresponding lubrication device
The invention relates to a method of lubricating transport systems or parts thereof, in particular guideways and rails in stretching units, and also to the use of a lubrication arrangement for carrying out the method and to an associated transport system with corresponding lubrication device.
Lubrication arrangements in which, for example, the running surfaces in transport systems is to be effected by droplet lubrication or oil mist lubrication have already been disclosed. During droplet lubrication, for example, lubricating oil is fed to the machine parts moving against one another in a rolling or sliding manner via arrangements which permit accurate proportioning of the oil quantity per lubricating point. In this case, the oil is fed to the points to be lubricated via a pressure generator or via tanks, oil droplet apparatuses and the like placed above the points to be lubricated. In the process, the quantity is distributed via proportioning valves or metering elements, a specific volume being delivered during each working stroke. In this case, the individual working strokes are separated from one another by idle times, during which no oil is delivered.
U.S. Pat. No. 5,634,531, for example, has disclosed an appropriately electrically controllable automatic lubrication arrangement. A piston is moved forward via an electrically activated screw spindle, and the free-flowing lubricant located in a pressure space is delivered via a discharge opening. In this case, the electric motor for feeding the pressure medium is connected to a control loop which is periodically activated for driving the motor in the abovementioned sense in order to deliver a next metered quantity of lubricant.
In a central lubrication arrangement for tension chains which has been disclosed by DD 148 356, provision is made for a piston pump to be driven via a motor, this piston pump drawing in lubricant from a tank via a suction line and the lubricant being fed to the corresponding lubricating point via outlets of the piston pump, preferably 6 to 12 outlets for 6 to 12 lubricating points, specifically via droplet indicators. In this case, each droplet indicator is assigned to a corresponding lubricating point or sprays the lubricating oil per stroke of the piston pump to the respectively associated lubricating point, i.e. a sliding surface or a joint pin. The speed of rotation of the piston pump and thus the number of strokes per minute can be firmly established via gear unit or coupling.
Against this background, the object of the present invention is to provide an improved method of lubricating transport systems and parts thereof, in particular corresponding parts of a stretching unit, and also an improved lubrication arrangement and a corresponding transport system with improved lubrication, in particular an improved method or an arrangement to the effect that a further reduction in the lubricant consumption becomes possible.
However, in all the methods disclosed by the prior art, it has now been found that, when the lubricant is being fed (through bores in the rail, for example, in the case of stretching units), the lubricant droplets produced, which discharge as a result, have a certain minimum size. As soon as a part to be lubricated which comes into contact with the oil droplet is moved over this lubricant, for example a running roller or a sliding element in the case of a stretching unit, most of the droplet volume is displaced or thrown off laterally and can therefore no longer come into effect. The present technical limit for metering is around 10 mm3 per metering point. At present, smaller quantities cannot be metered in this form. This is because the best lubricant [sic] systems up to now work with a pneumatic delivery in a pulsed operation at a comparatively long time interval, in which case the pulsing appears necessary in order to exceed a minimum pressure in order to actually deliver a very small droplet. If the pressure were to be reduced even further during the pulsing, the pressure, due to internal friction values, would be reduced in the lubricant passage system to such an extent that no more droplets would be delivered at the lubricant openings.
In contrast, the invention proposes continuous lubricant delivery and feed, i.e. with a marked reduction in the idle times provided in the prior art or even completely avoiding idle times in a cycle. According to the invention, a short interruption in the lubricant feed is only necessary when a lubricant pressure space has been completely emptied while using a corresponding lubrication arrangement, and the piston or pistons have to be briefly retracted and the tank has to be filled again.
In a preferred embodiment of the invention, the continuous lubricant delivery according to the invention is characterized in particular by the fact that the continuous guidance is nonetheless carried out directly, thus obviating the need for additional transfer systems which ultimately effect the lubrication and which are described in DE 22 54 729 B2, for example, as being necessary.
The quite fundamental and substantial difference between the method according to the invention and the prior art results just from the fact that, for example, the quotient of the active lubricating time and the idle or reloading time of a lubricant volume which is filled with lubricant and can be refilled with lubricant again after it has been emptied can amount to a value X=0.25 in the prior art, it being possible in the lubrication according to the invention for this figure to be greater not only by a factor of 10, 100 or 1000, for example, but even to be 5000 times and more greater, for example.
Marked advantages compared to previous methods are achieved by this method according to the invention. On the one hand, a drastic reduction in the lubricant consumption is obtained. Furthermore, if it is considered that very expensive special temperature-resistant oils have to be used in many installations, in particular in film stretching units, the financial savings can be seen immediately. On the other hand, the reduction in the lubricant consumption results in the quite fundamental further advantage that lubricant particles which are thrown off can thus cause less contamination and impairment, and thus the quality and cleanliness of the product to be manufactured are markedly improved. This is also in particular very important in the manufacture of plastic film.
It is also mentioned, only for the sake of completeness, that the spray lubrication known in principle in the prior art leads to no improvement in this respect, since the lubricant, in this case too, is not applied exactly to the lubricating point, lubricant is consequently likewise wasted, and in addition, again especially in the manufacture of plastic film, the plastic film is greatly contaminated by the mist of the discharging lubricant, this mist being finely distributed in the air.
An arrangement which is suitable in particular for continuous lubricant discharge over a long time is proposed in order to carry out the method.